1. Field Of The Invention
This invention relates to seals for long-term usage in oil and gas well tools and the like, and more particularly, to seals for sliding sleeve-type closures designed to maintain a sealing connection for relatively long time periods, such as the life of the well.
2. Description Of The Prior Art
Sealing of components in oil and gas wells is of critical importance, both during the operation of downhole tools and for use in portions of the tools which remain in the well after completion, testing and production. For example, well apparatus with sliding closures frequently must be sealed during operation, and this sealing engagement must be maintained substantially indefinitely.
Prior art seals such as elastomeric seals can have problems over time in that the elastomer may lose resiliency or shape memory which is necessary for the seal to oppose the imposed squeeze forces thereon. This is a particular problem with exposure to downhole chemical and higher temperature environments of oil and gas wells for long periods of time. A seal is therefore required that remains operative in these types of environments.
Metal-to-metal seals have been developed because they are not affected by the chemicals and temperatures that are usually encountered. However, metal-to-metal seals are normally only used as static seals or as safety backup seals to standard elastomeric rotational or sliding seals because they have not been proven to be particularly suitable for use in dynamic sealing applications. One factor in the use of metal-to-metal seals is that the contacted sealing surfaces must be machined particularly smoothly and be free of pits and scratches so that a positive seal may be maintained. Damage to these surfaces can be caused by galling and scratching as the metal seal moves across the seal surface, and in such cases leakage is likely.
The present invention solves these problems by providing a new seal which incorporates the best aspects of metal-to-metal seals and elastomeric seals. In another embodiment, an improved metal-to-metal seal is also used to solve these problems.